The present invention generally relates to a vertical type construction transistor, and more particularly, to a vertical type construction transistor for power amplification use.
Recently, demand for power amplification transistor in a microwave band has increased. For example, a heterojunction.multidot.bipolar.multidot.transistor (hereinafter referred to as "HBT") of a vertical type construction is provided (for example, N. L. Wang and others, "Superhigh Power Efficiency Operation of Emitter Common and Base Common HBT in 10 GHz" IEEE Transaction on Microwave Wave and Techniques, vol. 38, No. 10, pp. 1381-1389). As the HBT has a high gain and a low output conductance as compared with already developed GaAsFETs, the HBT it is watched as a means for realizing high efficiency amplifier.
As the above described HBT operates with high current density, it becomes inevitably higher. For proper operation, the heating of a junction portion (pn junction) formed on a basic plate surface has to be released out of the semiconductor basic plate with better efficiency. In the above described document, a means for releasing the heating of the junction portion onto the side of the basic plate reverse face side is provided. Namely, (1) the semiconductor basic plate is cut down thinly, and (2) a via hole (a hole extending through a basic plate surface side from a basic plate reverse face side) immediately under an electrode pulled out from the junction portion to the periphery with a metallic material, which has better thermal conductivity being buried into the via hole.
When the above described features (1), (2) have been adopted, the following problems are caused.
(i) In order to cut down the basic plate thinly and further, open a via hole, broken pieces are caused in the wafer so as to lower the yield. PA1 (ii) The above described via hole is subject to the restriction of the working precision and is separated by at least 5 .mu.m or more from the junction portion (heated location). Thus, it is difficult to effectively reduce the heat resistance. PA1 (iii) In the microwave band, an outgoing line from the junction portion has an inductance which cannot be neglected, and functions as feedback inductance so as to suffer a loss.
As many problems are caused like this, conventionally the HBT could not be developed as the power amplification use in the microwave band.